1. Field of the Invention
The invention relates to a construction method for synthetic-reinforced earthworks. More particularly, the inventions relates to a system of constructing a steep embankment that is suitable for greening.
2. Description of the Prior Art
Geosynthetic-reinforced retaining structures and steep embankments are composite structures that are constructed from fill, reinforcements, and an outer skin. Shear-resistant, well-graded and compactable gravel sand is used as the fill. The reinforcements are embedded in the fill and typically comprise high-tensile-strength geosynthetics, such as, primarily, geogrids, textiles, and composites. The so-called outer skin is applied to the air side of the retaining structure to complete the structure. This composite structure of fill and reinforcements is the actual support system that guarantees the structural stability of the retaining structure. The outer skin is a protective system that serves to protect the support system from external influences and thereby ensures the long-term stability of the overall structure.
Prior art DE 10 2004 014 539 A1 discloses a recent solution, namely a system for the erection of retaining structures and steep embankments suitable for greening. The system comprises pad support walls that bear and dissipate static and/or dynamic loads. These pad walls are constructed with high-tensile-strength geosynthetic reinforcements embedded in a compacted fill. A separate, three-dimensionally structured outer skin, filled with non-compacted soils or materials capable of supporting greening or plant growth, is used during erection of the system as a temporary abutment for the geosynthetic reinforcements. This outer skin absorbs the pressure that arises when the individual fill layers are compacted and provides lasting protection for the pad walls. The outer skin comprises a multitude of segments that include unilaterally, vertically concave rear-wall elements and exchangeable front elements. The round bulges of the pad walls formed by the geosynthetics and the compacted fill butt up against the curved rear-wall segments. At least two spacers or spacer elements, to which the front and rear-wall elements are affixed, and which are arranged spaced parallel from each other on the front element, are used. The spacer elements are, in turn, mounted in profiles, constructed preferably as U-rails, that are anchored in the underlying pad by soil nailing. This structure forms box-like cavities, into which soils suitable for greening or other materials may be filled.
All prefabricated elements of the outer skin are joined by way of a plug-in or snap-fit connector system, whereby the use of adapter pieces between the front elements and the spacer elements enables the construction of an outer skin that has different steepness angles and curvatures.
The segments of the outer skin correspond in their vertical dimensions to the thickness of the layers of fill to be introduced and compacted. The outer skin is thus constructed in layer form. The segments of the outer skin are preferably 40 cm high. The layers of the outer skin are usually offset to each other in a step-like arrangement.
The front element is constructed as a flexurally rigid, three-dimensional lattice structure which may incorporate a fixed greening structure. It is intended that the front element and likewise the spacers be made of a synthetic material which implies a proportion of renewable raw materials.
The side of the spacers where the rear-wall elements are affixed is curved concavely to correspond to the curvature of the rear-wall elements; the side where the front elements are affixed has an angle of inclination between 55 and 70 degrees. The rear-wall elements are preferably constructed of a biodegradable material or natural fibers.
The special form of the rear wall of the outer skin achieves significant reduction in the magnitude of vertical and horizontal changes in the form of the support system, due to improved force flow in the geosynthetic reinforcements. In addition to satisfying the requirements with regard to the durability of such a structure, in other words frost and UV resistance, as well as resistance to damaging external influences, the conditions for greening are significantly improved. The fact that fill and cultivation soil are strictly separated, enabling the latter to be introduced loosely, also improves greening. Finally, the segments of the outer skin permit variable structuring of the segments with respect to inclination, height and contour, whereby it is possible to replace them in the case of damage, without impairing the structural stability of the support system.
Further aspects of the prior art are presented in detail in DE 10 2004 014 539 A1.
A disadvantage of solution described above is that the concavely formed rear wall of the system entails considerable manufacturing effort, namely complex tools, and is thus relatively cost-intensive. In addition, a system of this complexity is not necessary in many of the situations which call for retaining structures and steep embankments suitable for greening. Simplifying the design and the manufacturing of the element is thus advantageous. The large amount of geosynthetics required, even for steep embankments of low height and inclination, calls for a new solution.
What is needed therefore is a structural system for the erection of steep embankments that reduces manufacturing costs. What is further needed is such a system that is capable of achieving complex shapes, yet quickly and easily assemblable. What is yet further needed is such a system that reduces the use of geosynthetics.